Map showing earthquake epicenters determined in this study (red circles), injection wells (squares and + symbols) in use since October 2006, seismograph stations (white triangles), and mapped faults (green lines). Circle sizes indicate quality of epicentral location, with large, medium and small sizes indicating qualities A, B and C. For injection wells, yellow squares are wells with maximum monthly injection rates exceeding 150,000 barrels of water per month (BWPM); white squares, exceeding 15,000 BWPM; + symbols, exceeding 1,500 BWPM. Credit: Cliff Frohlich/U. of Texas at Austin.
AUSTIN, Texas — Most earthquakes in the Barnett Shale region of North Texas occur within a few miles of one or more injection wells used to dispose of wastes associated with petroleum production such as hydraulic fracturing fluids, according to new research from The University of Texas at Austin. None of the quakes identified in the two-year study were strong enough to pose a danger to the public. The study by Cliff Frohlich, senior research scientist at the university's Institute for Geophysics, appears this week in the journal Proceedings of the National Academy of Sciences . "You can't prove that any one earthquake was caused by an injection well," says Frohlich. "But it's obvious that wells are enhancing the probability that earthquakes will occur." Frohlich analyzed seismic data collected between November 2009 and September 2011 by the EarthScope USArray Program, a National Science Foundation-funded network of broadband seismometers from the Canadian border to the Gulf of Mexico. Because of the high density of instruments (25 in or near the Barnett Shale), Frohlich was able to detect earthquakes down to magnitude 1.5, far too weak for people to feel at the surface. He found that the most reliably located earthquakes - those that are accurate to within about 0.9 miles (1.5 kilometers) - occurred in eight groups, all within 2 miles (3.2 kilometers) of one or more injection wells.
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